We are undertaking a pilot study to determine what laboratory studies best predict a therapeutic response to iron in one year old infants. This is the age at which iron deficiency is most common and at which there is greatest uncertainty about normative laboratory data. By determining which laboratory studies and values are predictive of a significant hemoglobin and MCV response we hope to find the most cost-effective means for screening infants for iron deficiency. In the iron deficient rat, we plan to study several non-heme-iron-containing enzymes in brain that were recently found to be depressed in terms of supporting phosphorylation in mitochondria of skeletal muscle. This should indicate what other non-heme iron compounds other than ferritin are affected in brain and how these might affect brain function. Behavioral studies require greater numbers of adult animals to confirm the indications that females have long term changes in behavior as a result to iron deficiency in early life.